(i) Field of the Invention
This invention relates to components for weighing scales and more particularly to torque arm mounting means for such weighing scales. More specifically, it relates to internally pivoted torque-transmitting arms for weigh-in-motion or for static weigh scales.
(ii) Description of the Prior Art
Presently available weighing scales generally include a fixed peripheral framework, and a central movable platform, connected to the peripheral framework and to a load cell which could translate vertical movement of the central movable platform with respect to the peripheral framework into a measure of the weight on the platform.
Present weigh scales with single load cells, especially those for weighing vehicles in motion, require torque-transmitting arms with exceptional rigidity. This is so because the pivot points of the pad and roller placed outside the torque-transmitting arms were designed to be massive and heavy. Weigh-in-motion scales requiring weight measurements of ten thousand pounds or more carried stabilizing torque-transmitting arms where the pivot point of the arms was in the range of seven and one-quarter inches apart. For this reason, torque arms were designed with six inch diameter seamless tubing and a three-quarter inch wall. Also, prior art weigh scales, being of welded construction, required too much skill and judgment during assembly. The heavy torque arms, weighing as much as one hundred and eighty-five pounds each, required extra lifting equipment during installation.
One important fact to consider in the design of such weigh scales is the response time, especially when the scale is to be used for weighing vehicles in motion, but is also important for weighing vehicles or other articles when at rest. Factors which contribute to response time of such a weigh scale include: deflections of the load platform under loading due to lack of rigidity of the platform-supporting structure, friction in the interconnections linking the load platform and base structure, and vertical travel of the load platform for activating the load cell. Improved response time for vehicle scales is difficult to achieve since improvements in rigidity necessary for rapid response tend to result in increased friction which shows response.
Many proposals have been made concerning platform-supporting mechanisms which were believed to provide the required rigidity. These included the use of four peripheral torque-transmitting bars in conjunction with the following interconnecting mechanisms: pin and links, rack and gear, loop strap, and chain and sprocket. However, it was found that all of these would have too much friction to be suitable for weighing moving vehicles. U.S. Pat. No. 3,354,973 issued Nov. 28, 1967 to J. C. Farquhar illustrates typical mechanisms similar in principle to some of those previously evaluated.
An improvement thereon was provided by Dyck in U.S. Pat. No. 4,064,955 issued Dec. 27, 1977. That patent provided a scale for weighing vehicles in motion having a load-supporting platform, a fixed base structure, and means for interconnecting the platform with the base structure for allowing vertical motion of the platform. Such interconnecting means were torque-transmitting bars arranged around the perimeter of the load-supporting platform with specifically recited support and roller assemblies associated with each end of each torque-transmitting bar. A load-measuring device was also provided which operated with low vertical travel, the load cell being disposed between the platform and the base structure.
While such mounting means for the torque arms were suitable, it was found that they still did not provide adequate rigidity for all contemplated uses. Because of the intricate nature of the weigh scale, the heavy torque arms and the complicated nature of assembly, litte could be done in the field in terms of repair and adjustment. Accordingly, it is the purpose of this invention to provide an improved torque arm and scale assembly.